1. Field of the Invention
The present invention relates to a 3D circuit module such as a memory card which is used as a recording medium for mobile digital devices, and which is suitable as a circuit module to be densely mounted with thin electronic components like a memory IC chip in a predetermined area. The present invention also relates to a multilayer 3D circuit module formed of a plurality of such 3D circuit modules, a mobile terminal device using the 3D or multilayer 3D circuit module, and methods for manufacturing the 3D and multilayer 3D circuit modules.
2. Background Art
A conventional circuit module board used for a memory card is disclosed in Japanese Patent Unexamined Publication No. 2002-207986 (hereinafter, Patent Document 1).
FIGS. 13A and 13B are cross sectional views of a circuit module board disclosed in Patent Document 1.
FIG. 13A shows circuit module board 1030 in which electronic components 1020 such as an IC chip are mounted on only one side of wiring board 1010 made of epoxy resin or the like. FIG. 13B shows circuit module board 1070 in which electronic components 1050 and 1060 are mounted on both sides of wiring board 1040.
As shown in the cross sectional view of FIG. 14, predetermined electrodes 1020A of circuit module board 1030 and predetermined electrodes 1050A and 1060A of circuit module board 1070 are connected with each other by solder 1090 via conductive balls 1080 such as Cu balls.
Circuit module boards 1030 and 1070 thus connected are stacked on base board 1100 so as to form circuit module board 1110 having a 3D circuit structure such as a memory card.
However, in conventional circuit module board 1030 having electronic components 1020 mounted on only one side of wiring board 1010, electronic components 1020 thus mounted may be warped by the difference in linear expansion coefficient between wiring board 1010 and electronic components 1020 or electrodes 1020A. This susceptibility to warpage makes it difficult to reduce circuit module board 1030 in thickness.
On the other hand, in circuit module board 1070 having electronic components 1050 and 1060 mounted on both sides of wiring board 1040, either electronic components 1050 or electronic components 1060 are mounted on one side first and the other are mounted on the other side later. This way of mounting causes a difference in thermal history between mounting electronic components 1050 and mounting electronic components 1060, and results in a difference in adhesive force.
Moreover, the 3D circuit with multilayer structure is formed by connecting between circuit module boards 1030 and 1070 with solder 1090 via conductive balls 1080. Consequently, conductive balls 1080, which are difficult to be supplied at one time to electrodes 1020A, 1050A and 1060A, must be supplied individually, thus decreasing production efficiency.
In addition, these circuit module boards must be arranged with clearance therebetween to avoid contact damage or other damage, making it difficult to reduce the thickness and to increase the density of a 3D circuit with multilayer structure.